1. Field of the Invention
The present invention relates to a method and apparatus for controlling a fusing operation. More particularly, the present invention relates to controlling the temperature of a fuser having a hot roller and a cooperating backup roller to fuse an image onto a media using an estimated temperature of the backup roller.
2. Description of Related Prior Art
In an electrophotographic image forming apparatus, such as a printer or copier, a latent image is formed on a light sensitive drum and developed with toner. The toner image is then transferred onto a medium, such as a sheet of paper, and is subsequently passed through a fuser where heat is applied to melt the toner and fuse it to the medium. The fuser includes a hot fuser roller cooperating with a backup roller to form a nip through which the toned media passes. The hot roller is provided with an internal heater, such as a tungsten-filament lamp, and a temperature sensor for providing a temperature signal to a print engine for controlling the temperature of the fusing operation to a predetermined target temperature. Additionally, in order to facilitate fuser warm-up and temperature control, it is known to provide the backup roller with an internal heater, and to include an additional temperature sensor providing a temperature signal for controlling the temperature of the backup roller. However, in order to minimize the cost of the fuser it is desirable to provide a heater element and temperature sensor for only the hot roller, controlling the power to the heater element of the hot roller to compensate for energy absorbed and given off by the backup roller during operation of the fuser. In any event, accurate control of the fusing temperature to a predetermined target temperature is important in order to meet gloss, fuse grade, transmittance and release requirements for the fusing operation.
Various control techniques have been proposed to compensate for the energy absorbed by the backup roller, as well as to adjust the fusing conditions for heat energy that may be conveyed to the backside of the media from the backup roller during the fusing operation. For example, it is known to control the hot roller of a fuser at an elevated temperature during printing of an initial quantity of media, and then lower the temperature of the hot roller for fusing of subsequent media sheets. Such control provides an initial increased amount of energy as the backup roller heats to a steady state temperature, and then adjusts the temperature of the hot roller for the subsequent fuser operation with the backup roller transferring energy to the media for fusing the later part of a print job having multiple sheets of media. The steady state temperature of the backup roller and the rate at which the backup roller absorbs energy vary depending on the type of media being processed and the throughput of the fuser. For example, heavier media will absorb more energy from the hot roller, resulting in the backup roller temperature rising at a slower rate than for a lighter weight media. Similarly, a higher throughput rate, i.e., smaller gaps between successive media, will reduce the rate of energy transfer to the backup roller, resulting in a lower backup roller steady state temperature. In controlling the print job, the print engine specifies a process speed for a particular job, however, the throughput of media passing through the fuser varies depending various factors including the rate at which the printer""s processor can process the image data. For example, a job including a large amount of image data, such as may occur when printing graphic image data, may result in large gaps between successive media sheets producing a low throughput and resulting in a higher steady state temperature.
U.S. Pat. No. 5,701,554 discloses a fixing apparatus including a controller for controlling a target temperature of a heating member and for estimating the amount of heat transferred to a pressurizing member. The pressurizing member cooperates with the heating member to define a nip through which a sheet carrying an unfixed toner image is passed for fusing the toner to the sheet. The temperature of the pressurizing member is indirectly determined based on the amount of electric power supplied to the heating member and the temperature of the heating member, which provides a measure of the amount of heat absorbed from the heating member by the pressurizing member. The temperature of the heating member is considered to deviate from the target temperature in proportion to the amount of heat dissipated from the heating member. This proportional relationship is used to estimate the temperature of the pressurizing member with reference to the temperature of the heating member. The controller uses the estimated temperature of the pressurizing member to adjust the target temperature of the heating member to maintain a desired fixing temperature at the nip.
There remains a need for an effective method and apparatus for controlling the temperature of a fuser having a hot roller and a cooperating backup roller wherein the temperature of only one of the rollers is monitored, and the temperature of the other roller may be accurately estimated to maintain the fuser temperature at a desired value.
A method of controlling a fuser is provided in which a steady state temperature of a pressure member, such as a backup roller, is estimated for use in controlling the temperature of the fuser. In particular, a throughput of media through the fuser is measured and a corresponding backup roller steady state temperature is predicted for controlling the fuser to avoid exceeding a predetermined maximum temperature for the backup roller.
In accordance with one aspect of the invention, a method is provided for controlling a fuser having a heating member and a pressure member cooperating with the heating member to fuse an image onto a media, the method comprising conveying media through the fuser; detecting a rate at which the media is processed through the fuser; and controlling the fuser in response to the detected processing rate to limit a temperature of the pressure member to a value below a predetermined maximum temperature.
In accordance with another aspect of the invention, a method is provided for controlling a fuser having a heating member and a pressure member cooperating with the heating member to fuse an image onto a media, the method comprising determining a current pressure member temperature; conveying media through the fuser; detecting a rate at which the media is processed through the fuser; determining a predicted steady state temperature for the pressure member based on the detected rate and for a particular mode of operation; calculating a pressure member temperature change for a predetermined time interval; calculating a new estimated pressure member temperature equal to the current pressure member temperature increased or decreased by the pressure member temperature change; and setting the current pressure member temperature equal to the new estimated pressure member temperature and repeating the calculation for a new estimated pressure member temperature.
In accordance with yet a further aspect of the invention, a fuser is provided comprising a heating member; a pressure member cooperating with the heating member to form a nip therebetween for fusing an image onto a media passing through the nip; a detecting element detecting passage of media processed through the nip to provide a detected processing rate; and means for controlling the fuser with reference to the detected processing rate to limit a temperature of the pressure member to a value below a predetermined maximum temperature.
Other features and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.